Updates from the MUSE experiment

Several recent experiments addressed the proton-radius puzzle. However, the experimental determination of the proton charge radius from lepton-scattering or hydrogen-spectroscopy data remains challenging, and the present results are still in tension. The MUon Scattering Experiment (MUSE) at the piM1 beam line of the Paul Scherrer Institute aims to clarify the issue. The experiment uses electron and muon beams with momenta up to 210 MeV/c and covers a four-momentum transfer range from Q² of approximately 0.002 to 0.08 GeV². It measures high-precision lepton-proton elastic scattering cross sections and determines and directly compares form factors and charge-radii for both particle species. Radiative corrections are an important source of systematic uncertainty in form-factor extractions, and MUSE will study those. A downstream photon calorimeter helps investigate and suppress contributions from initial-state radiation, and the use of positively and negatively charged leptons allows for the study of two-photon-exchange effects. Pions are a component of the beam-particle mix at the secondary beam line. While they are a background for the lepton-scattering aspect of the experiment, they allow for an opportunistic measurement of the pion-proton elastic scattering cross sections. MUSE aims to complete production data-taking in 2025. The status of the experiment will be reviewed.